Force transmission belts, which are also referred to as drive belts and which form endless loops in the operational state, can be configured as flat belts, V-belts, V-ribbed belts and toothed belts.
The surface of these force transmission belts and of a toothed belt in particular has to have good gliding properties and be wear resistant. Such a surface is achieved through a coating with or without textile cover ply. When the force transmission belt is operated under an oil atmosphere, an additional requirement is good oil resistance to protect the coating and the rubber mixture(s) underneath from the penetration of oil.
Mixtures of a flexible polymeric layer with fillers are typically used for this because they are both readily glidable and oil resistant.
DE4400434A1, EP0662571A1 and U.S. Pat. No. 6,419,775 describe woven fabric coatings that consist of a polyurethane coating with particulate fluoropolymers and provide good abrasion resistance. The two-component coating mass has a low viscosity, penetrates into the woven fabric relatively deeply and undergoes crosslinking to form an abrasion-resistant layer. However, these layers have an open structure and so are insufficiently abrasion-resistant for many applications. Furthermore, owing to this open structure they are not oil-resistant and owing to the polyurethanes used their thermal stability is insufficient for many applications.
The lack of heat resistance is taken up in U.S. Pat. No. 7,946,940 where 1,2-diols are disclosed as not being as heat-resistant as the longer-chain 1-omega diols. There are again issues with abrasion and oil resistance.
DE102008013570A1 describes coating systems for woven fabric surfaces of force transmission belts, wherein the coating contains a polyisocyanurate-polyurea formed from an isocyanate having at least two NCO groups as base component. This coating exhibits outstanding glidability coupled with good heat resistance, but possesses unfavorable processability owing to the sensitivity of the coating masses. Moreover, because of the solvents needed, coating to deeply penetrate the woven fabric is not possible.
Gliding systems for belts having uninterrupted surfaces are described in U.S. Pat. No. 6,739,997, U.S. Pat. No. 7,985,152, U.S. Pat. No. 7,749,118 and EP1881229A1 for dry applications and in U.S. Pat. No. 7,749,118 and WO2007036960A1 for applications in oil. What is common to the systems described in the references cited is that they consist of a coating composed of an elastomeric matrix and a glidant which is present in less than 50% quantity and preferably is fluoropolymer containing. The elastomeric matrix is always based on commercially available polymers which, owing to their high molecular weight of >5000 g/mol, are incapable of penetrating into the woven fabric if applied with no or almost no solvent. The layer thus covers the woven fabric, but does not penetrate thereinto, leading to a slight breakdown of the woven fabric and, on the other hand, in use, to cracks through which oil, for example, is easily able to penetrate.
An improved heat resistance and an improved resistance to the skipping of teeth are said to be ensured by the toothed belt disclosed in U.S. Pat. No. 5,234,387. In this toothed belt, the tooth rubber and the backing rubber comprise a hydrogenated nitrile rubber polymer crosslinked with organic peroxide, and a co-crosslinker comprising N,N′-m-phenylenedimaleimide in combination with a compound from various acrylates, isocyanurates, mellitates, phthalates, carboxylates or metal salts. Advantages in respect of abrasion and/or oil resistance are not known for this.